Highly polymerizable N-vinlycarboxylic acid amide and production process thereof

ABSTRACT

A highly polymerizable N-vinylcarboxylic acid amide having an N-1,3-butadienylcarboxylic acid amide content of 30 ppm or less, a process for producing the same, and a process for producing a homopolymer of N-vinylcarboxylic acid amide or a copolymer thereof with another copolymerizable monomer using the same. Also, a highly polymerizable N-vinyl-carboxylic acid amide is produced by thermal cracking or catalytic cracking of N-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acid amide, wherein the N-vinyl-carboxylic acid amide content of the N-(1-alkoxyethyl)-carboxylic acid amide or ethylenebiscarboxylic acid amide is 10 wt % or less.

This is a divisional of application Ser. No. 08/996,819, filed Dec. 23,1997, now U.S. Pat. No. 5,892,115, which is a divisional of applicationSer. No. 08/585,919, filed Jan. 16, 1996, now U.S. Pat. No. 5,789,619,the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a highly polymerizableN-vinylcarboxylic acid amide, a production process thereof and a processfor producing a high molecular weight polymer of N-vinylcarboxylic acidamide using the same. More specifically, the present invention providesan N-vinylcarboxylic acid amide having improved polymerizability and aprocess for producing the same. The N-vinylcarboxylic acid amide isadvantageously used in industry as a monomer for the production of anN-vinylcarboxylic acid amide polymer, which polymer is used as acoagulant, a liquid absorbent or a thickener. The present invention alsoprovides a process for producing the polymer. Furthermore, the presentinvention provides a high-quality N-vinylcarboxylic acid amide that isuseful as a raw material for industrial chemicals or medical products invarious fields.

BACKGROUND OF THE INVENTION

A large number of methods for producing an N-vinylcarboxylic acid amidehave hitherto been proposed. For example, a method is known where anN-(1-alkoxyethyl)-carboxylic acid amide as an intermediate is producedfrom a carboxylic acid amide, acetaldehyde and an alcohol, and anN-vinylcarboxylic acid amide is synthesized by cracking or catalyticcracking of the product. Another useful method for synthesizing anN-vinylcarboxylic acid amide includes synthesizing an ethylidenebiscarboxylic acid amide from acetaldehyde and a carboxylic acid amide.This product is then cracked into a carboxylic acid amide and anN-vinylcarboxylic acid amide.

In these methods, a purification step, such as distillation, extractionand recrystallization of the resulting N-vinylcarboxylic acid amide isprovided. For example, JP-A-61-286069 (the term "JP-A" as used hereinmeans an "unexamined published Japanese patent application") disclosesan extraction separation using water and an aromatic hydrocarbon. Thisis because distillation fails to prevent mingling of formamide as anunreacted raw material into the N-vinylformamide. Furthermore,JP-A-63-132868 discloses cooling crystallization from a mixed organicsolvent, JP-A-2-188560 discloses extraction using an aqueous inorganicsalt solution and an aromatic hydrocarbon, and U.S. Pat. No. 4,401,516discloses extractive distillation using a polyhydric alcohol.

On the other hand, an N-vinylcarboxylic acid amide polymer is obtainedby polymerizing an N-vinylcarboxylic acid amide alone or copolymerizingwith another monomer. The polymer is used as a coagulant, a liquidabsorbent or a thickener, and in any case the polymer must have a highmolecular weight. However, it has been difficult to obtain anN-vinylcarboxylic acid amide which consistently exhibits goodpolymerizability in any of the uses described above.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a highly polymerizableN-vinylcarboxylic acid amide having good and improved polymerizability.

Another object of the present invention is to produce a high molecularweight N-vinylcarboxylic acid amide polymer.

As a result of extensive investigations on the production process of anN-vinylcarboxylic acid amide having good polymerizability, the presentinventors have found that a high molecular weight polymer can beproduced using an N-vinylcarboxylic acid amide having anN-1,3-butadienylcarboxylic acid amide content of 30 ppm or less,preferably 10 ppm or less, more preferably 1 ppm or less, to therebyachieve the present invention.

More specifically, the present invention provides a highly polymerizableN-vinylcarboxylic acid amide, wherein the N-vinylcarboxylic acid amidehas an N-1,3-butadienylcarboxylic acid amide content of 30 ppm or less,a production process thereof, and a process for producing a highmolecular weight polymer of an N-vinylcarboxylic acid amide using thesame.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the relationship between viscosity and theN-1,3-butadienylacetamide content of crude N-vinylacetamide (NVA) asmeasured following the procedure of Example 1. The viscosity is ameasure of the degree of polymerizability.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in detail below.

The N-vinylcarboxylic acid amide for use in the present invention isrepresented by formula (I):

    CH.sub.2 ═CH--NR.sup.1 --COR.sup.2                     (I)

(wherein R' and R each represents a hydrogen atom or an alkyl grouphaving from 1 to 5 carbon atoms). Examples thereof includeN-vinylformamide, N-methyl-N-vinylformamide, N-vinylacetamide,N-methyl-N-vinylacetamide, N-vinylpropionamide,N-methyl-N-vinylpropionamide, N-vinylbutylamide andN-vinylisobutylamide. Among these, N-vinylformamide and N-vinylacetamideare preferred and N-vinylacetamide is more preferred.

The N-1,3-butadienylcarboxylic acid amide is represented by formula(II):

    CH.sub.2 ═CH--CH═CH--NR.sup.1 --COR.sup.2          (II)

(wherein R¹ and R² each has the same meaning as defined above) andincludes cis and trans forms which are present as geometrical isomersthereof.

In the present invention, a highly polymerizable N-vinylcarboxylic acidamide is obtained by setting the content of N-1,3-butadienylcarboxylicacid amide in the crude N-vinylcarboxylic acid amide to 30 ppm or less,but a desired high polymerizability may be obtained by setting thecontent preferably to 10 ppm or less, and more preferably to 1 ppm orless. If the content exceeds the above-described range, highpolymerizability is difficult to achieve.

This is verified, for example, by the relationship (FIG. 1) between thecontent of N-1,3-butadienylacetamide in crude N-vinylacetamide andviscosity (degree of polymerizability).

There is no particular limitation on the production process of anN-vinylcarboxylic acid amide which is used in the process for producinga highly polymerizable N-vinylcarboxylic acid amide of the presentinvention, as long as the crude N-vinylcarobxylic acid amide thusobtained has an N-1,3-butadienylcarboxylic acid amide content in excessof 30 ppm, and in some cases, in excess of 10 ppm or 1 ppm. However, inone preferred embodiment, the N-vinylcarboxylic acid amide is producedthrough dealcoholization of an N-(1-alkoxyethyl)carboxylic acid amide ordealcoholization of an N-(1-alkoxyethyl)carboxylic acid amide obtainedas an intermediate from carboxylic acid amide, acetaldehyde and alcoholor from carboxylic acid amide and acetaldehyde dialkylacetal. In thiscase, the dealcoholization reaction is preferably conducted by thermalcracking or catalytic cracking. In another preferred embodiment, theN-vinylcarboxylic acid amide is produced through cracking of ethylidenebiscarboxylic acid amide or cracking of an ethylidene biscarboxylic acidamide obtained as an intermediate from acetaldehyde and carboxylic acidamide. In this case, the ethylidene biscarboxylic acid is cracked into acarboxylic acid amide and an N-vinylcarboxylic acid amide. In thepresent invention, a highly polymerizable N-vinylcarboxylic amide havingan N-1,3-butadienylcarboxylic acid amide content of 30 ppm or less maybe produced by a purification processing method where anN-1,3-butadienylcarboxylic acid amide is reduced or removed from thecrude N-vinylcarboxylic acid amide, or by a purification processingmethod where an N-1,3-butadienylcarboxylic acid amide or a precursorthereof is reduced or removed from the production raw material orintermediate of N-vinylcarboxylic acid amide.

A method of reducing or removing an N-1,3-butadienylcarboxylic acidamide from the crude N-vinylcarboxylic acid amide is described below.

The purification processing method for reducing or removing anN-1,3-butadienylcarboxylic acid amide from the crude N-vinylcarboxylicacid amide includes, for example, a physical purification processingmethod of processing the crude N-vinylcarboxylic acid amide or asolution thereof by rectification, a recrystallization method, pressurecrystallization or treatment with an adsorbent such as activated carbon,and a purification processing method using chemical conversion ofN-1,3-butadienylcarboxylic acid amide, such as a method of processingN-1,3-butadienylcarboxylic acid amide with p-benzoquinone using aDiels-Alder reaction and a method of processing the 1,3-butadienyl groupusing selective hydrogenation. These methods may be used eitherindividually or in combination. Other than the above-described methods,any method may be used if the N-1,3-butadienylcarboxylic acid amide iseasily separated from the N-vinylcarboxylic acid amide or chemicallyconverted.

The method for removing or reducing the amount ofN-1,3-butadienylcarboxylic acid amide from the crude N-vinylcarobxylicacid amide is described in greater detail below.

In the process of the present invention, there is no particularlimitation on the distillation apparatus for use in separating byrectification, and a plate column or packed column having a theoreticalplate number of from 1 to 50 may be used. However, a rectifying columnis preferably used which causes little pressure loss and has excellentrectifiability, and examples thereof include a packed column using aregular filling. The distillation is preferably conducted at atemperature that is as low as possible because the N-vinylcarboxylicacid amide is readily deteriorated due to heat. Accordingly, thedistillation is conducted under a reduced pressure of from 0.01 to 100mmHg.

The rectification may be conducted either continuously ordiscontinuously, however, a continuous operation is preferred in view ofproductivity and safety in operation. The reflux ratio is notparticularly limited and can be set according to the content ofN-1,3-butadienylcarboxylic acid amide, the kind of N-vinylcarboxylicacid amide and the capabilities of the distillation column. However, thereflux ratio is generaly from 0.1 to 20, and preferably from 0.5 to 10.

In the process of the present invention, when the separation is made bya recrystallization method comprising cooling a crude N-vinylcarboxylicacid amide, the N-vinylcarboxylic acid amide may be directly cooled, ora recrystallization solvent which does not react with theN-vinylcarboxylic acid amide and having an appropriate solubility may beused. Examples of the recrystallization solvent include an aromatichydrocarbon such as benzene, toluene and xylene; an aliphatichydrocarbon such as pentane, cyclopentane, hexane, cyclohexane andheptane; an alcohol such as methanol, ethanol, n-propyl alcohol,isopropyl alcohol, n-butanol, isobutanol, sec-butanol, tert-butanol andcyclohexanol; a halogenated hydrocarbon such as chloroform andchlorobenzene; a ketone such as acetone, methyl ethyl ketone andcyclohexanone; an ester such as methyl acetate, ethyl acetate, propylacetate and butyl acetate; an ether such as diethyl ether; an amide suchas N,N-dimethylformamide and N,N-dimethylacetamide; and adimethylsulfoxide. Toluene, cyclohexane, methanol and isopropyl alcoholare preferred. These solvents may also be used in combination. Thecooling temperature varies depending upon the kind and the amount of theN-vinylcarboxylic acid amide and the recrystallization solvent, but itis usually from -20 to 50° C., preferably from -10 to 40° C.

The crystallization apparatus for use in the present invention is notparticularly limited with respect to its structural form and may beeither a continuous system or a batch system. Also, the crystallizationmethod may either employ heat exchange with a cooling medium, orconcentration and cooling of the solvent upon evaporation.

The apparatus for separating crystals for use in the present inventionis also not particularly limited. An apparatus using vacuum pressure orthe application of pressure, or an apparatus using gravity orcentrifugal force may be used.

In the present invention, a solid-liquid separator which combinescrystallization and separation in the same apparatus may also be used.Preferred examples of the apparatus include, in the case of not using acrystallization solvent, a pressure crystallizer, a falling filmcrystallizer (e.g., a fractional crystallization apparatus) and a towertype continuous crystallization purifier (e.g., a BMC or back mixingcolumn crystallizer apparatus). In the case of filtering a highconcentration slurry, an automatic Nutsche filter such as a Rosemundfilter is preferably used.

In the process of the present invention, when the crudeN-vinylcarboxylic acid amide is separated by treating with an adsorbentsuch as activated carbon, the adsorbent for use in the present inventionis not particularly limited as long as it selectively adsorbs theN-1,3-butadienylcarboxylic acid amide in comparison with theN-vinylcarboxylic acid amide. Examples of the adsorbent includeactivated carbon, clays, alumina, silica, zeolite and adsorptive resin,and among these, activated carbon is preferred.

In the adsorption operation of the present invention, the crudeN-vinylcarboxylic acid amide may be placed into direct contact with theadsorbent. Alternatively, the crude solution may be dissolved in asolvent which does not react with the N-vinylcarboxylic acid amide andwhich has an appropriate solubility, and then placed into contact withthe adsorbent. Examples of the solvent include water and those describedabove with respect to the method of recrystallization, and whenactivated carbon is used as an adsorbent, water and methanol areparticularly preferred. The ratio of the solvent to the crudeN-vinylcarboxylic acid amide is not particularly limited, however, whenwater or methanol is used as the solvent, it is preferably from 0 to10:1 (by weight), more preferably from 0.1 to 3:1 (by weight).

The adsorption temperature suitable for conducting the adsorptionoperation of the present invention varies depending upon the kind ofadsorbent, but it is preferably from -20 to 100° C., more preferablyfrom 0 to 80° C. If the adsorption temperature is lower than -20° C.,diffusion into the pores of the adsorbent is considerably retarded todisadvantageously prolong the adsorption time. If the temperature ishigher than 100° C., stability of the N-vinylcarboxylic acid amide islowered and at the same time, the equilibrium adsorption quantity isgreatly reduced.

The adsorption method of the present invention is not particularlylimited with respect to the structural form thereof, but may either be acontinuous system or a batch system.

In the present invention, the content of N-1,3-butadienylcarboxylic acidamide in the N-vinylcarboxylic acid amide may be reduced to 30 ppm orless by chemically processing the crude N-vinylcarboxylic acid amidesolution. There is no particular limitation on the chemical reaction tobe used as long as it uses the difference in reactivity between theN-vinylcarboxylic acid amide and the N-1,3-butadienylcarboxylic acidamide. For example, the reaction with a diene is highly active but thereaction with a monoene is inactive.

The method of processing the crude N-vinylcarboxylic acid amide solutionusing a Diels-Alder reaction, and the method of processing the solutionusing selective hydrogenation are described below.

In the present invention, when the crude N-vinylcarboxylic acid amidesolution is processed using a Diels-Alder reaction, the processing isconducted by allowing a dienophilic compound (dienophile) in theDiels-Alder reaction to be present in the crude N-vinylcarboxylic acidamide solution. The dienophilic compound of the present invention is notparticularly limited as long as it is a compound commonly used as adienophilic compound in the Diels-Alder reaction, more specifically, acompound which is selected from α,β-unsaturated compounds substituted byone or more electron attractive group(s) and which does not react withthe N-vinylcarboxylic acid amide. Examples of the dienophilic compoundinclude an unsaturated carboxylic ester;

such as acrylic ester maleic ester and fumaric ester, an unsaturatedketone such as methyl vinyl ketone and p-benzoquinone; an unsaturatednitrile such as acrylonitrile; and an unsaturated imide such as maleicacid imide. Among these, p-benzoquinone is preferred. The amount of thedienophilic compound is not particularly limited as long as it isequivalent to or more than the amount of the N-1,3-butadienylcarboxylicacid amide contained in the crude N-vinylcarboxylic acid amide. However,the molar ratio of the dienophilic compound to theN-1,3-butadienylcarboxylic acid amide contained in the crudeN-vinylcarboxylic acid amide solution is generally from 1 to 100equivalents, and preferably from 1.2 to 10 equivalents.

In the present invention, when the crude N-vinylcarboxylic acid amidesolution is processed by a Diels-Alder reaction, the crudeN-vinylcarboxylic acid amide may be directly contacted with thedienophilic compound. Alternatively, the crude solution may be dissolvedin a solvent which does not react with the N-vinylcarboxylic acid amideand has an appropriate solubility, and then subjected to a Diels-Alderreaction. Examples of the solvent include the solvents described abovewith respect to the adsorption method of the present invention.Furthermore, although a catalyst is not required when the crudeN-vinylcarboxylic acid amide solution is processed by a Diels-Alderreaction in the present invention, those known to have catalyticactivity in the Diels-Alder reaction and which do not react with theN-vinylcarboxylic acid amide may be used. Examples of the catalystinclude Lewis acids such as aluminum trichloride, boron trifluoride andlanthanide complex.

The reaction temperature suitable for the Diels-Alder reaction of thepresent invention varies depending upon the kind of the dienophiliccompounds used, but it is preferably from -20 to 100° C., and morepreferably from 0 to 80° C. If the reaction temperature is lower than-20° C., the reaction rate is too slow, whereas if the reactiontemperature exceeds 100° C., stability of the N-vinylcarboxylic acidamide is disadvantageously reduced.

The N-vinylcarboxylic acid amide solution processed by a Diels-Alderreaction of the present invention contains a Diels-Alder adduct producedby the Diels-Alder reaction, but this compound has almost no harmfuleffect on the polymerization of the N-vinylcarboxylic acid amide. TheDiels-Alder adduct produced in the present invention has a low vaporpressure as compared with the N-1,3-butadienylcarboxylic acid amide.Accordingly, if the N-vinylcarboxylic acid amide solution is purified bydistillation after processing by a Diels-Alder reaction of the presentinvention, the Diels-Alder adduct can be separated more easily thanN-1,3-butadienylcarboxylic acid amide that is removed by distillationalone. In other words, the compound can be separated using simpledistillation equipment.

The processing of the crude N-vinylcarboxylic acid amide using ahydrogenation reaction of the present invention is conducted bycontacting the crude N-vinylcarboxylic acid amide with hydrogen in thepresence of a catalyst. The catalyst is not particularly limited as longas it has general activity in the selective hydrogenation reaction ofolefins, however, the catalyst preferably has high diene hydrogenationselectively when a monoolefin and a diene are present together. Examplesof the catalyst include a Pd series, Co series or Ni--Co--Cr seriesmetal or a modified product of these metals provided on alumina,activated carbon or silica and among these, Pd-alumina, Pd--Ag-alumina,Pd--Pb-alumina, Pd--Cr-alumina and Pd-alumina-based catalysts arepreferred. When Pd is used as the metal component, the carried amountthereof is preferably from 0.001 to 5 wt %, more preferably from 0.01 to1 wt %. If the carried amount is less than 0.001 wt %, the reaction rateis extremely slow, whereas if it exceeds 5 wt %, N-ethylacetamideresulting from hydrogenation of the N-vinylcarboxylic acid amidedisadvantageously increases.

In the present invention, when the N-vinylcarboxylic acid amide isprocessed by a hydrogenation reaction, the N-vinylcarboxylic acid may bedirectly contacted with hydrogen, or may be dissolved in a solvent,which does not react with the N-vinylcarboxylic acid amide and which hasan appropriate solubility, and then subjected to a hydrogenationreaction. Examples of the solvent include the solvents described abovewith respect to the adsorption method of the present invention. Amongthese, an alcohol is preferred, and methanol and isopropyl alcohol areparticularly preferred. The reaction temperature suitable for thehydrogenation reaction of the present invention varies depending uponthe kind of catalyst used, but it is preferably from -20 to 100° C.,more preferably from 0 to 80° C. If the reaction temperature is lowerthan -20° C., the reaction rate is extremely slow, whereas if it exceeds100° C., the stability of the N-vinylcarboxylic acid amide is reduced.

The hydrogen partial pressure suitable for the selective hydrogenationreaction of the present invention is from 0.01 to 100 kg/cm², preferablyfrom 0.5 to 50 kg/cm². If the hydrogen partial pressure is less than0.01 kg/cm², the reaction rate is extremely slow, whereas if it exceeds100 kg/cm², the production of N-ethylacetamide resulting fromhydrogenation of N-vinylcarboxylic acid amide increases and theequipment becomes more expensive.

When the catalyst is charged and fluidized, the proper conditions ofliquid space velocity vary depending upon the hydrogen partial pressure,the reaction temperature and the content of N-1,3-butadinenylcarboxylicacid amide, but the liquid space velocity is preferably from 0.05 to1000. If it exceeds 1000, the conversion of N-1,3-butadienylcarboxylicacid amide is insufficient, whereas if it is less than 0.05, thereaction efficiency is reduced.

The reaction method for use in the present invention may either beconducted continuously or batchwise, and the reaction vessel is notparticularly limited in its structural form. Any of gas-solid contact,gas-liquid-solid contact and solid-liquid contact may be used, however,a solid-liquid reactor capable of uniform contact of the raw materialwith the catalyst under relatively mild conditions is preferred. Whenthe solid-liquid reaction is conducted, hydrogen is previously dissolvedin the crude N-vinylcarboxylic acid amide solution so as to supply thehydrogen necessary for the reaction.

After the hydrogenation reaction, the reaction solution contains aby-product accompanying the product produced by the hydrogenationreaction. Methods for purifying the reaction solution include, forexample, rectification, recrystallization by cooling and pressurecrystallization of the solution, and these methods may be usedindividually or in combination. Other than these methods, any method maybe used without particular restriction if the by-product and theN-vinylcarboxylic acid amide can be easily separated.

As described above, the N-1,3-butadienylcarboxylic acid amide has a cisform and a trans form and due to difference in the physical propertiesor reactivity of these, the degree of separation may vary in the presentinvention.

In that case, a cis-trans isomerization reaction of theN-1,3-butadienylcarboxylic acid amide may be conducted under appropriatereaction conditions in combination with the above-described operationssuch as separation.

In any case, the N-vinylcarboxylic acid amide causes solvolysis orhydrolysis when an acid is present. Accordingly, it is preferred toplace auxiliary facilities for use in the present invention, such as aproduction apparatus, a separation apparatus, a raw material tank, aproduct container and a filtrate tank, under an atmosphere of inert gas(nitrogen) or dry air. Furthermore, in order to prevent a hydrolysisreaction of N-vinylcarboxylic acid amide, a slight amount of a dryingagent such as magnesium sulfate may be added to the raw material.

When a base is present, a dimerization reaction results. Accordingly,the pH of the N-vinylcarboxylic acid amide solution is preferablyadjusted prior to the distillation and adsorption operation to a pH offrom 3 to 11, preferably from 4 to 10, more preferably from 5 to 6. Whenthe crude N-vinylcarboxylic acid amide solution is acidic, the pH isadjusted by adding a basic compound. Examples of the basic compoundinclude sodium salts such as sodium carbonate, sodium hydrogencarbonate,sodium hydroxide, sodium (hydrogen)-phosphate and sodium acetate,potassium salts such as potassium carbonate, potassiumhydrogencarbonate, potassium hydroxide, potassium (hydrogen)phosphateand potassium acetate, and aromatic amines such asN-phenyl-a-naphthylamine, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine,N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine,N-phenyl-N'-isopropyl-p-phenylenediamine,N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine,N-phenyl-N'-cyclohexyl-p-phenylenediamine,N,N'-diphenyl-p-phenylenediamine, N,N'-di-β-naphthyl-p-phenylenediamine,N,N'-bis(1,4-dimethylpentyl)-p-phenylene-diamine,N,N'-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine,N,N'-bis(1-methylheptyl)-p-phenylenediamine andN-phenyl-N'-(p-toluenesulfonyl)-p-phenylenediamine, with sodiumhydroxide being particularly preferred.

The addition amount of the basic compound is preferably from 1 to 10,000ppm, more preferably from 10 to 1,000 ppm. If the addition amountexceeds 10,000 ppm, in the case of an inorganic salt, the entire amountis not dissolved and no additional effect is expected from the excessamount. In case of an aromatic amine, it is difficult to completelyremove the aromatic amine at the purification step, and thepolymerizability of N-vinylcarboxylic acid amide is reduced. If theaddition amount is less than 1 ppm, almost no stabilizing effect isobtained.

When the crude N-vinylcarboxylic acid amide solution is basic, theadjustment is conducted by adding an acidic compound. Examples of theacidic compound include acidic inorganic compounds such as hydrochloricacid, sulfuric acid, nitric acid, phosphoric acid and a salt thereof,and acidic organic compounds including carboxylic acids such as aceticacid, phthalic acid and citric acid, carbolic acids such as phenol,hydroquinone and catechol, and salts thereof.

Among the methods for use in the present invention, a method forreducing or removing the N-1,3-butadienylcarboxylic acid amide or aprecursor thereof contained in the production raw material orintermediate of N-vinylcarboxylic acid amide is described below. Theprecursor content is expressed in terms of the content ofN-1,3-butadienylcarboxylic acid amide when all precursors are convertedinto N-1,3-butadienylcarboxylic acid amide.

In the process of the present invention, the production raw material orintermediate of N-vinylcarboxylic acid amide includesN-(1-alkoxyethyl)carboxylic acid amide, dialkylacetal andethylidenebiscarboxylic acid amide. Examples of the alkoxyl group inN-(1-alkoxyethyl)carboxylic acid amide and dialkylacetal include analiphatic alkoxyl group such as methoxy, ethoxy, n-propyl, isopropoxy,n-butoxy and sec-butoxy. Examples of the carboxylic acid amide group inN-(1-alkoxyethyl)carboxylic acid amide and ethylidenebiscarboxylic acidamide include formamide, N-methylformamide, acetamide,N-methylacetamide, propionamide, butyramide and isobutyramide. Examplesof the corresponding compound include: as theN-(1-alkoxyethyl)carboxylic acid amide, N-(1-methoxyethyl)acetamide,N-(1-methoxyethyl)formamide, N-(1-ethoxyethyl)acetamide,N-(1-ethoxyethyl)formamide, N-(1-iso-propoxyethyl)acetamide andN-(1-isopropoxyethyl) formamide; as the dialkylacetal, dimethylacetal,diethylacetal and diisopropylacetal; as the ethylidenebiscarboxylic acidamide, ethylidenebisacetamide, ethylidenebisformamide,ethylidenebis-(N-methylformamide) and ethylidenebispropionamide.

An N-(1-alkoxyethyl)carboxylic acid amide or an ethylidenebiscarboxylicacid amide is converted into an N-vinylcarboxylic acid amide by a knownmethod such as thermal cracking or catalytic cracking. The reactionconditions are, for example, such that a gas phase or a liquid phase isused. The reaction temperature is from 60 to 600° C., the reaction timeis from 0.3 second to 2 hours and the reaction pressure is from 0.1 mmHgto atmospheric pressure. Examples of the catalyst used in case ofcatalytic cracking include an alkali metal salt of carboxylic acid suchas potassium acetate and an oxide of an alkali metal or an alkalineearth metal, such as magnesium oxide.

The N-1,3-butadienylcarboxylic acid amide is produced upon eliminationof two alcohol molecules induced by the thermal cracking or catalyticcracking of N-(1,3-dialkoxybutyl)carboxylic acid amide, or uponelimination of alcohol and carboxylic acid amide induced by the thermalcracking or catalytic cracking of 3-alkoxybutylidenebiscarboxylic acidamide. The N-(1,3-dialkoxybutyl)carboxylic acid amide and3-alkoxybutylidenebiscarboxylic acid amide are produced by the reactionof 1,1,3-trialkoxybutane with carboxylic acid amide.

Accordingly, in the present invention, examples of the precursor ofN-1,3-butadienylcarboxylic acid amide include 1,1,3-trialkoxybutane,N-(1,3-dialkoxybutyl)carboxylic acid amide and3-alkoxybutylidenebiscarboxylic acid amide, and examples of the alkoxylgroup and the carboxylic acid amide group in these precursors includethose described above for the precursor of N-vinylcarboxylic acid amide.Therefore, the 1,1,3-trialkoxybutane includes 1,1,3-trimethoxybutane,1,1,3-triethoxybutane and 1,1,3-triisopropoxybutane; theN-(1,3-dialkoxybutyl)carboxylic acid amide includesN-(1,3-dimethoxybutyl)acetamide, N-(1,3-dimethoxybutyl)formamide,N-(1,3-diethoxybutyl)acetamide, N-(1,3-diethoxybutyl)-formamide,N-(1,3-diisopropoxybutyl)acetamide andN-(1,3-diisopropoxybutyl)formamide; and the3-alkoxybutylidenebiscarboxylic acid amide includes3-methoxybutylidenebisacetamide, 3-methoxybutylidenebisformamide,3-ethoxybutylidenebisacetamide, 3-ethoxybutylidenebisformamide,3-isopropoxybutylidenebisacetamide and3-isopropoxy-butylidenebisformamide.

The embodiment for reducing the content of N-1,3-butadienylcarboxylicacid amide or a precursor thereof in the production raw material orintermediate of N-vinylcarboxylic acid amide to 30 ppm or less includes,for example, a rectification method, a recrystallization method bycooling the precursor solution of N-vinylcarboxylic acid amide, apressure crystallization method of the precursor, a physical adsorptionmethod by treating the precursor with an adsorbent such as activatedcarbon and a method of chemically processing the precursor, and thesemethods may be used individually or in combination. Other methods may beused without particular limitation as long as theN-1,3-butadienylcarboxylic acid amide or a precursor thereof can beeasily separated from the production raw material or intermediate of theN-vinylcarboxylic acid amide.

Furthermore, as a result of extensive investigations on the process forproducing an N-vinylcarboxylic acid amide having good polymerizability,the present inventors have found that an N-vinylcarboxylic acid amidefor use in the synthesis of a high molecular weight polymer is producedwhen, in producing an N-vinylcarboxylic acid amide by thermal crackingor catalytic cracking of N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide, the N-vinylcarboxylic acid amidecontent of the N-(1-alkoxyethyl)-carboxylic acid amide orethylidenebiscarboxylic acid amide is reduced to 10 wt % or less and thepH of a 33 wt % aqueous solution (hereinafter simply referred to as"pH") of the N-(1-alkoxyethyl)carboxylic acid amide orethylenebiscarboxylic acid amide is adjusted to from 5 to 10.

More specifically, the present invention provides a process forproducing an N-vinylcarboxylic acid amide having good polymerizability,wherein, when an N-vinylcarboxylic acid amide is produced by thermalcracking or catalytic cracking of N-(1-alkoxyethyl)carboxylic acid amideor ethylidenebiscarboxylic acid amide, the N-vinylcarboxylic acid amidecontent of the N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide is reduced to 10 wt % or less,preferably S wt % or less, more preferably 3 wt % or less, the pH of theN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide is adjusted to from 5 to 10, preferably from 6 to 8, morepreferably from 6.3 to 7.5, and still more preferably, theN-vinylcarboxylic acid amide content is reduced to 3 wt % or less and atthe same time, the pH is adjusted to from 6.3 to 7.5.

There are various reasons why the N-(1-alkoxyethyl)carboxylic acid amideor ethylidenebiscarboxylic acid amide generally contains more than 10 wt% of N-vinylcarboxylic acid amide.

One reason is that when a reaction solution containingN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide obtained by the above-described synthesis method is purified andseparated by a distillation operation or the like, a part of theN-(1-alkoxyethyl)carboxylic acid or ethylidenebiscarboxylic acid amideis cracked into N-vinylcarboxylic acid amide.

Another reason is that when an N-vinylcarboxylic acid amide issynthesized by thermal cracking or catalytic cracking ofN-(1-alkoxylethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide and the N-vinylcarboxylic acid is separated, the unreactedN-(1-alkoxylethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide which contains N-vinylcarboxylic acid is recycled for cracking.

A method for reducing the N-vinylcarboxylic acid amide content ofN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide to 10 wt % or less is described below.

The method is not particularly limited as long as it is a method forreducing the N-vinylcarboxylic acid amide content ofN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide to 10 wt % or less. The method includes, for example, theprocessing of N-(1-alkoxyethyl)carboxylic acid amide,ethylidenebiscarboxylic acid amide or a solution of these by arectification method, an azeotropic distillation method, arecrystallization method or a pressure crystallization method, and thesemethods may be used individually or in combination. Other than thesemethods, any method may be used without any particular restriction if itis a method where N-(1-alkoxyethyl)-carboxylic acid amide orethylidenebiscarboxylic acid amide and N-vinylcarboxylic acid amide canbe easily separated.

The embodiment for reducing the N-vinylcarboxylic acid amide content ofN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide to 10 wt % or less is described in greater detail below.

In the process of the present invention, the distillation apparatus usedfor separating by a rectification method is not particularly limited anda plate column or packed column having a theoretical plate number offrom 1 to 50 may be used, but it is preferable to use a rectificationcolumn which causes little pressure loss and has excellent rectificationcapabilities. An example of such a rectification column is a packedcolumn using a regular filling. N-(1-alkoxyethyl)carboxylic acid amide,ethylidenebiscarboxylic acid amide and N-vinylcarboxylic acid amide arereadily deteriorated due to heat. Thus, it is preferable to effectdistillation at as low a temperature as possible. Accordingly, thedistillation is conducted under a reduced pressure of from 0.01 to 100mmHg.

The present invention may be conducted either continuously or batchwise,however, in view of productivity and operation safety, a continuousoperation is preferred. The reflux ratio is not particularly limited andcan be set according to the content and kind of N-vinylcarboxylic acidamide and the capabilities of the distillation column. However, the reflux ratio is generally from 0.1 to 20, and preferably from 0.5 to 10.

In the process of the present invention, when the separation is effectedaccording to a recrystallization method by cooling theN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide solution, the recrystallization solvent, apparatus and processdescribed above with respect to the recrystallization method forN-vinylcarboxylic acid amide can be used.

A method for adjusting the pH of N-(1-alkoxyethyl)-carboxylic acid amideor ethylidenebiscarboxylic acid amide to from 5 to 10 is describedbelow.

The pH of N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide becomes less than 5 due to thepresence of a carboxylic acid such as acetic acid therein. Although itis not clearly known why the carboxylic acid is mixed therein, it isconsidered that this results from oxidation of acetaldehyde used in thesynthesis of N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide, or the production of carboxylic acidamide by solvolysis.

The method for adjusting the pH of N-(1-alkoxyethyl)carboxylic acidamide or ethylidenebiscarboxylic acid amide to from 5 to 10, is notparticularly limited. The method includes, for example, the processingof N-(1-alkoxyethyl)carboxylic acid amide, ethylidenebiscarboxylic acidamide or a solution of these by a rectification method, an azeotropicdistillation method, a recrystallization method, a pressurecrystallization method, a physical method using treatment with anadsorbent or a chemical method using neutralization by an acid or abase, and these methods may be used either individually or incombination.

Among these methods, the physical method including processing by arectification method, an azeotropic distillation method, arecrystallization method or a pressure crystallization method may bemade in the same manner as described above with respect to the removalof N-vinylcarboxylic acid amide. The method using an adsorbent includesa method where an anion exchange resin is used as an adsorbent.

Examples of the basic compound for use in neutralizing an acid as achemical method include a sodium salt such as sodium carbonate, sodiumhydrogencarbonate, sodium hydroxide, sodium (hydrogen)phosphate andsodium acetate, and a potassium salt such as potassium carbonate,potassium hydrogencarbonate, potassium hydroxide, potassium(hydrogen)phosphate and potassium acetate.

When the N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide solution is basic, the pH thereof isadjusted by adding an acidic compound. Examples of the acidic compoundinclude acidic inorganic compounds such as hydrochloric acid, sulfuricacid, nitric acid, phosphoric acid and a salt thereof, and acidicorganic compounds including carboxylic acids such as acetic acid,phthalic acid and citric acid, carbolic acids such as phenol,hydroquinone and catechol, and salts thereof.

The conversion of N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide into N-vinylcarboxylic acid amide iseffected by the above-described thermal cracking or catalytic cracking.

In the present invention, the N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide causes solvolysis or hydrolysis whenan acid is present. Accordingly, it is preferred to install auxiliaryfacilities for use in the present invention, such as a productionapparatus, a separation apparatus, a raw material tank, a productcontainer and a filtrate tank, in an atmosphere of inert gas (nitrogen)or dry air. Furthermore, in order to prevent a hydrolysis reaction ofN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide, a slight amount of a drying agent such as magnesium sulfate maybe added to the raw material.

In the present invention, when an N-vinylcarboxylic acid amide isproduced by thermal cracking or catalytic cracking ofN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide, the N-vinylcarboxylic acid amide content of theN-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylic acidamide is reduced to 10 wt % or less, preferably 5 wt % or less, morepreferably 3 wt % or less, the pH of the N-(1-alkoxyethyl)carboxylicacid amide or ethylidenebiscarboxylic acid amide is adjusted to from 5to 10, preferably from 6 to 8, more preferably from 6.3 to 7.5, andstill more preferably, the N-vinylcarboxylic acid amide content isreduced to 3 wt % or less and at the same time, the pH is adjusted tofrom 6.3 to 7.5, whereby an N-vinylcarboxylic acid amide having thedesired polymerizability is obtained. If the N-vinylcarboxylic acidamide content exceeds the above described range, it tends to bedifficult to obtain a highly polymerizable N-vinylcarboxylic acid amideby thermal cracking or catalytic cracking of N-(1-alkoxyethyl)carboxylicacid amide or ethylidenebiscarboxylic acid amide. Also, if the pHexceeds the above-described range, it tends to be difficult to obtain ahighly polymerizable N-vinylcarboxylic acid amide by thermal cracking orcatalytic cracking of N-(1-alkoxyethyl)carboxylic acid amide orethylidenebiscarboxylic acid amide.

The present invention provides a process for producing a homopolymer orcopolymer of N-vinylcarboxylic acid amide using the above-describedN-vinylcarboxylic acid amide.

By using a highly polymerizable N-vinylcarboxylic acid amide in whichthe crude N-vinylcarboxylic acid amide has an N-1,3-butadienylcarboxylicacid amide content of 30 ppm or less, a homopolymer of a high molecularweight N-vinylcarboxylic acid amide or a copolymer thereof with othercopolymerizable monomer can be obtained.

As used herein, "highly polymerizable" means that the viscosity asmeasured following the procedure of Example 1 is 30 cps or more,preferably 60 cps or more, and also means that the peak achieving timeas measured following the procedure of Example 13 is 15 hours or less,preferably 10 hours or less. The term "high molecular weight" means aweight average molecular weight of 500,000 or more, preferably 1,000,000or more.

Specific examples of representative monomers copolymerizable with theN-vinylcarboxylic acid amide of the present invention include:

an alkali metal salt such as a sodium salt or potassium salt of acrylicacid or methacrylic acid; an alkyl ester of the alkali metal salt, suchas methyl ester, ethyl ester, propyl ester, butyl ester, pentyl ester,hexyl ester, heptyl ester, octyl ester, nonyl ester, decyl ester,stearyl ester and palmityl ester; a hydroxy lower alkyl ester of thealkali metal salt, such as hydroxyethyl ester, hydroxypropyl ester andhydroxybutyl ester; a lower alkyl ester substituted by a loweralkylamino group of the alkali metal salt, such as dimethylaminomethylester, dimethylaminoethyl ester, dimethylaminopropyl ester,dimethylaminobutyl ester, diethylaminomethyl ester, diethylaminoethylester, diethylaminopropyl ester and diethylaminobutyl ester; a loweralkyl ester halide (the halide being preferably chloride or bromide)substituted by a quaternary ammonium group of the alkali metal salt,such as trimethylammonioethyl ester halide, trimethylammoniopropyl esterhalide, triethylammonioethyl ester halide and triethylammoniopropylester halide; an amide of the alkali metal salt; an amide substituted bya lower alkylamino group of the alkali metal salt, such asdimethylaminomethylamide, dimethylaminoethylamide,dimethylaminoproylamide, dimethylaminobutylamide,diethylaminomethylamide, diethylaminoethylamide, diethylaminopropylamideand diethylaminobutylamide; a lower alkylamide substituted by aquaternary ammonium group of the alkali metal salt, such astrimethylammonioethylamide halide, triethylammoniopropylamide halide,triethylammonioethylamide halide and triethylammoniopropylamide halide;a lower alkylamide substituted by a sulfonic acid or an alkali metalsulfonic acid of the alkali metal salt, such as sulfomethylamide,sulfoethylamide, sulfopropylamide, sulfobutylamide, sodiumsulfomethylamide, sodium sulfoethylamide, potassium sulfopropylamide,potassium sulfobutylamide, potassium sulforethylamide, potassiumsulfoethylamide, potassium sulfopropylamide and potassiumsulfobutylamide; an acrylonitrile; a vinyl ether such as methyl vinylether, ethyl vinyl ether, propyl vinyl ether and a butyl vinyl ether; avinyl ketone such as methyl vinyl ketone and ethyl vinyl ketone; a lowervinyl carboxylate such as vinyl acetate and vinyl propionate; a maleicanhydride; a maleic acid; sodium maleate; and potassium maleate.

Among these preferred are (meth)acrylic acid , sodium (meth) acrylate,methyl (meth) acrylate, ethyl (meth)acrylate, propyl (meth)acrylate ,butyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl (meth)acryl (methacrylatminoethyl(meth)acrylate, trimethylaminoethyl (meth)acrylate chloride, acrylamide,sodium sulfopropylacrylamide, sodium sulfobutylacrylamide,acrylonitrile, methyl vinyl ether, ethyl vinyl ether, methyl vinylketone, ethyl vinyl ketone, vinyl acetate, N-vinyl-2-pyrrolidone andmaleic anhydride. As used herein, "(meth)acrylic acid" means acrylicacid or methacrylic acid.

In the present invention, a crosslinking monomer or crosslinking agentwhich is a compound having two or more unsaturated groups in onemolecule, may be used as a monomer copolymerizable withN-vinylcarboxylic acid amide.

The polymerization process is not necessarily limited and conventionallyknown processes may be used. Usually, a solution polymerization process,a reverse-phase suspension polymerization process or a reverse-phaseemulsion polymerization process is preferably used.

For example, in the solution polymerization process, monomer componentsand a crosslinking agent are uniformly dissolved in water, an organicsolvent or a mixed solvent of these, the dissolved oxygen in the systemis removed by vacuum deaeration or displacement by an inactive gas suchas nitrogen or carbon dioxide gas and then, a polymerization initiatoris added to the system to start the reaction. The polymerizationinitiation temperature is usually approximately from -10 to 60° C. andthe reaction time is approximately from 1 to 10 hours.

The N-1,3-butadienylcarboxylic acid amide of the present invention isverified and identified by mass spectra (an electron impact method and achemical ionization method), an infrared light absorption spectrum andan ultraviolet light absorption spectrum. For example,N-1,3-butadienylacetamide is identified as follows.

Physical properties of N-1,3-butadienylacetamide:

Mass spectrum (electron impact method): 111, 69, 54, 43

Mass spectrum (chemical ionization method): 112

Infrared light absorption spectrum (cm⁻¹):

3099, 1732, 1654, 1471

Ultraviolet light absorption spectrum (nm): 237, 276

In the present invention, the quantitative analysis ofN-1,3-butadienylcarboxylic acid amide is preferably made by high-speedliquid column chromatography, but the present invention not limited tothis method. For example, the following operating conditions of ahigh-speed liquid column chromatography are preferred. Unless otherwiseindicated, the quantitative analysis was conducted under theseconditions in the Examples of the present invention.

Column: SHODEX® SIL5B (Showa Denko K.K.)

Eluate: n-Hexane/isopropyl alcohol (9/1), 1 mL/min

Detector: Ultraviolet detector, 254 nm

The present invention will be described below in greater detail byreferring to the following Examples and Comparative Examples, however,the present invention should not be construed as being limited thereto.

EXAMPLE 1

To a three-necked flask (200 ml) with a thermometer and a dryice-ethanol trap, 5.9 g (0.1 mol) of acetamide, 40 g (0.67 mol) ofisopropyl alcohol, 2.16 g (15 mmol) of ethylidenebisacetamide and 14.6 g(0.1 mol) of acetaldehyde diisopropylacetal were added, and the mixturewas stirred and dissolved at a temperature of from 45 to 48° C. until itbecame uniform. A solution containing 0.43 g (0.1 wt % based on thecharge) of concentrated sulfuric acid dissolved in 2 g (33 mmol) ofisopropyl alcohol (the same in the following examples) was added andafter stirring, 17.6 g (0.4 mol) of acetaldehyde was added theretothrough a dropping funnel over a period of 3 minutes. After the droppingaddition, the mixture was allowed to react at 50° C. for 3 hours toneutralize the catalyst. The reaction mixture was then analyzed by gaschromatography to find that the acetamide conversion was 88%, theselectivity of N-(1-propoxyethyl)acetamide was 94% and the selectivityof ethylidenebisacetamide as a by-product was 5.3%. From the resultingreaction solution, N-(1-propoxyethyl)acetamide was obtained bydistillation under reduced pressure and thermally cracked intoN-vinylacetamide and isopropyl alcohol at 450° C. and a residence timeof 1 second. The cracked solution was cooled to 20° C. and the mothersolution was separated therefrom at 1800 kg/cm² and 20° C. in ahigh-pressure crystallizer. As a result, N-vinylacetamide in a purity of99.9% and having an N-1,3-butadienyl content of 1 ppm was obtained. Inorder to evaluate the polymerizability of the N-vinylacetamide,distillated water was added thereto to give a concentration of 17 wt %and after displacement by nitrogen, 500 ppm of V-50(N,N'-azobis-(2-amidinopropane) dihydrochloride was added thereto andthe container was dipped in a constant-temperature water bath of 45° C.After 10 minutes, the system was diluted by 9 wt % of a 1% aqueoussolution of hydroquinone and the viscosity was measured at 30° C. and arevolution number of 30 rpm using a BL-type (rotary) viscometer andfound to be 130 cps.

COMPARATIVE EXAMPLE 1

The thermally cracked solution obtained in Example 1 was subjected tosimple distillation at a pressure of 0.5 mmHg to provideN-vinylacetamide in a purity of 97.5% and having anN-1,3-butadienylacetamide content of 200 ppm. The polymerizabilityevaluation was conducted in the same manner as in Example 1, and theviscosity was found to be 10 cps or less.

EXAMPLE 2

Synthesis of acetal:

Into the fifth stage from the top of a glass-made Oldershaw-typerectification column having 25 stages, methanol containing 0.5 wt % ofsulfuric acid was introduced in an amount of 180 g per hour and into thefifteenth stage from the top, acetaldehyde was introduced in an amountof 27 g per hour. At the bottom of the rectification column, a 500ml-volume flask having placed therein 100 g of water was provided andheated at 100° C. to extract the content of the flask in an amount of 29g per hour. The solution extracted from the flask containedsubstantially no organic matter. From the top of column, 221 g/h of adimethylacetal-methanol mixture was extracted at a reflux ratio of 2.The distillate contained substantially no water and aldehyde. Theacetaldehyde conversion was 100% and the yield of dimethylacetal was100%.

Separation of acetal:

Into the first stage from the top of a glass-made Oldershaw-typerectification column having 25 stages, n-hexane was introduced in anamount of 56 g per hour and into the tenth stage from the top,dimethylacetal containing 28 wt % of methanol was introduced in anamount of 71 g per hour. The column was heated so that the temperatureof the column top was maintained at 50° C. at a reflux ratio of 6. Atthe lower part of the rectification column, a 500 ml-volume flask havingplaced therein 100 g of dimethylacetal was provided and heated bydipping it in an oil bath at 110° C. to thereby extract the content ofthe flask in an amount of 47 g per hour. The solution extracted from theflask was dimethylacetal substantially free of n-hexane and containing0.3% of methanol. From the top of column, 80 g/h of adimethylacetal-methanol-n-hexane mixture was extracted. The distillateand the bottom product each contained substantially no water oracetaldehyde.

Synthesis of N-(1-methoxyethyl)acetamide:

The high-purity dimethylacetal obtained in the acetal separation processand the dimethylacetal containing methanol obtained in the methanolrecovery process were mixed, and dry acetamide was dissolved therein toprepare a reaction raw material solution ofacetamide/dimethylacetal/methanol at a molar ratio of 1/20/3. Thissolution was introduced from the lower part of a reaction tube having aninner diameter of 40 mm charged with 60 ml of a strongly acidic ionexchange resin Amberlist 15, in an amount of 5 ml per hour. Into thejacket of the reaction tube, hot water at 55° C. was circulated tocontrol the reaction temperature to 55° C. The reaction solutionobtained from the exit at the upper portion of the reaction vessel wassubjected to quantitative analysis and, as a result, it was found thatthe reaction solution had a molar composition comprising approximatelyacetamide/dimethyl-acetal/methanol/MEA of 0/19/4/0.9, the acetamideconversion was 98% and the yield of N-(1-methoxyethyl)acetamide (MEA)was 90%.

Recovery of acetal:

The reaction solution obtained in the synthesis step ofN-(1-methoxyethyl)acetamide was fed to a thin film-type continuous flashevaporator with a jacket having a heating area of 0.04 m² under areduced pressure of 100 mmHg, in an amount of 600 g per hour. In thejacket, a heating medium was circulated. A residue on evaporationsubstantially comprising N-(1-methoxyethyl)acetamide was obtained in anamount of 17 g per hour. A solution comprising dimethylacetal containing7 wt % of methanol with the volatile components being condensed wasobtained in an amount of 583 g per hour.

Recovery of methanol:

Into the tenth stage from the top of a glass-made Oldershaw-typerectification column having 25 stages, the dimethylacetal fraction ofdistillate containing 7 wt % of methanol obtained in the acetal recoverystep was introduced in an amount of 200 g per hour. The column washeated so that the temperature of the column top was maintained at 58°C. at a reflux ratio of 6. At the lower potion of the rectificationcolumn, a 500 ml-volume flask was provided and heated by dipping it inan oil bath at 110° C. to extract the content of the flask in an amountof 185 g per hour. The solution extracted from the flask wasdimethylacetal containing 5.6 wt % of methanol. From the column top, adimethylacetal-methanol azeotropic mixture (methanol: 24 wt %) wasextracted in an amount of 15 g per hour.

Synthesis of N-vinylacetamide:

The solution substantially comprising N-(1-methoxyethyl)acetamideobtained in the acetal recovery step was fed into a stainless steelreaction tube having an inner diameter of 20 mm and a total length of 6m, which was under a reduced pressure of 100 mmHg and heated at 450° C.,in an amount of 20 ml per minute. The mixture of N-vinylacetamide andmethanol -produced by the thermal cracking reaction was condensed in acondenser provided at the exit of the reaction tube and recovered. Theconversion of N-(1-methoxyethyl)-acetamide was 92%.

Concentration of N-vinylacetamide:

Into the tenth stage from the top of a glass-made Oldershaw-typerectification column having 10 stages, the reaction solution obtained inthe synthesis step of N-vinylacetamide was introduced in an amount of200 g per hour. The pressure was 200 mmHg and the column was heated sothat the temperature of the column top was maintained at 40° C. at areflux ratio of 2. A 500 ml-volume flask was provided at the lowerportion of the rectification column and heated by dipping in an oil bathat 80° C. to extract the content of the flask in an amount of 155 g perhour. The solution extracted from the flask was a crude N-vinylacetamidesolution containing 94 wt % of N-vinylacetamide. From the column top,methanol was extracted in an amount of 45 g per hour. The crudeN-vinylacetamide contained 70 ppm of N-1,3-butadienylacetamide.

Purification of N-vinylacetamide:

The crude N-vinylacetamide solution obtained in the concentration stepof N-vinylacetamide was introduced into the fifth stage from the top ofa glass-made oldershaw-type rectification column having 10 stages andrectification was conducted under a reduced pressure of 0.15 mmHg and ata reflux ratio of 3. As a result, N-vinylacetamide in a purity of 98%and containing 4 ppm of N-1,3-butadienylacetamide was obtained. Thepolymerizability of the resulting N-vinylacetamide was evaluated in thesame manner as in Example 1, and the viscosity was found to be 100 cps.

EXAMPLE 3

The crude N-vinylacetamide containing 70 ppm ofN-1,3-butadienylacetamide obtained in the concentration step ofN-vinylacetamide in Example 2 was adjusted to 50° C. and the mothersolution was separated therefrom at 1,800 kg/cm² and 50° C. in ahigh-pressure crystallizer. As a result, N-vinylacetamide in a purity of99.9% and having an N-1,3-butadienylacetamide content of 1 ppm or lesswas obtained. The polymerizability of the resulting N-vinylacetamide wasevaluated in the same manner as in Example 1, and the viscosity wasfound to be 150 cps.

EXAMPLE 4

The methanol solution of N-vinylacetamide containing 70 ppm ofN-1,3-butadienylacetamide obtained in the synthesis step ofN-vinylacetamide in Example 2 was introduced into a column charged withactivated carbon at a LHSV of 2 Hr-¹ and room temperature. The resultingsolution contained 9 ppm of N-1,3-butdienylacetamide. The resultingsolution was subjected to simple distillation under reduced pressure.The polymerizability of the distilled N-vinylacetamide was evaluated inthe same manner as in Example 1, and the viscosity was found to be 70cps.

EXAMPLE 5

To 50 parts by weight of N-vinylacetamide containing 200 ppm ofN-1,3-butadienylacetamide obtained in Comparative Example 1, 50 parts byweight of toluene was added and dissolved at 40° C. in a nitrogenatmosphere. After cooling the mixture to 4° C., the precipitatedcrystals were separated by filtration and dried under reduced pressure.The resulting N-vinylacetamide contained 8 ppm of N-1,3-butadienylacetamide. The polymerizability of this product wasevaluated in the same manner as in Example 1, and the viscosity wasfound to be 80 cps.

EXAMPLE 6

To the methanol solution of N-vinylacetamide containing 70 ppm ofN-1,3-butadienylacetamide obtained in the synthesis step ofN-vinylacetamide in Example 2, p-benzoquinone was added to give aconcentration of 97 ppm (1.5 equivalent to theN-1,3-butadienylacetamide) and stirred at room temperature for 1 hour.The reaction solution contained 9 ppm of N-1,3-butadienylacetamide. Thesolution was subjected to simple distillation under reduced pressure.The polymerizability of the distilled N-vinylacetamide was evaluated inthe same manner as in Example 1, and the viscosity was found to be 70cps.

EXAMPLE 7

Five grams of solid catalyst comprising 0.5 wt % of palladium carried onan alumina carrier and 50 g of crude N-vinylacetamide containing 70 ppmof N-1,3-butadienylacetamide, 55 wt % of N-vinylacetamide, 15 wt % ofN-(1-methoxyethyl)-acetamide, 7 wt % of acetamide and 20 wt % ofmethanol were placed in a 200 ml-volume flask and reacted in a hydrogenatmosphere at room temperature for 30 minutes while stirring. Aftercompletion of the reaction, the catalyst was separated by filtrationfrom the reaction solution and the filtrate was analyzed. TheN-1,3-butadienylacetamide was analyzed by HPLC and other components wereanalyzed by gas chromatography. The reaction solution had anN-1,3-butadienylacetamide content of 1 ppm or less and contained 0.4 wt% of N-ethylacetamide.

After removing methanol by distillation under reduced pressure,N-vinylacetamide was crystallized in a high-pressure crystallizer undera pressure of 2,000 kg/cm and the mother solution was separated at 40°C. The resulting N-vinylacetamide had a purity. of 99.3 wt % and anN-1,3-butadienylacetamide content of 1 ppm or less. The polymerizabilitywas evaluated in the same manner as in Example 1, and the viscosity wasfound to be 160 cps.

EXAMPLE 8

A solid catalyst (2.5 g) comprising 0.5 wt % of palladium carried on analumina carrier was charged into a hydrogenation reactor in a nitrogenatmosphere. Under the nitrogen atmosphere, 95 kg of crudeN-vinylacetamide containing 400 ppm of N-1,3-butadienylacetamide, 55 wt% of N-vinylacetamide, 15 wt % of N-(1-methoxyethyl)acetamide and 20 wt% of methanol was circulated in the reaction vessel at a liquid spacevelocity (LHSV) of 60 Hr⁻¹ for 6 hours. The reaction solution had anN-1,3-butadienylacetamide content of 1 ppm or less and contained 0.3 wt% of N-ethylacetamide.

After removing methanol by distillation under reduced pressure from theresulting reaction solution, the mother solution was separated in ahigh-pressure crystallizer at 1,800 kg/cm² and 30° C. As a result,N-vinylacetamide in a purity of 99.5 wt % and having anN-1,3-butadienylacetamide content of 1 ppm or less was obtained.

The polymerizability of the resulting N-vinylacetamide was evaluated inthe same manner as in Example 1, and the viscosity was found to be 170cps.

EXAMPLE 9

A solid catalyst (25 g) comprising 0.5 wt % of palladium carried on analumina carrier was charged in a hydrogenation reaction vessel in anitrogen atmosphere and crude N-vinylacetamide containing 400 ppm ofN-1,3-butadienylacetamide, 55 wt % of N-vinylacetamide, 15 wt % ofN-(1-methoxyethyl)acetamide, 7 wt % of acetamide and 20 wt % of methanolwas circulated therein. The reaction solution had anN-1,3-butadienylacetamide content of 1 ppm or less and contained 0.5 wt% of N-ethylacetamide.

After removing methanol from the resulting reaction solution, the mothersolution was separated in a high-pressure crystallizer at 1,800 kg/cm²and 30° C. As a result, N-vinylacetamide in a purity of 99.5 wt % andhaving an N-1,3-butadienylacetamide content of 1 ppm or less wasobtained.

The polymerizability of the resulting N-vinylacetamide was evaluated inthe same manner as in Example 1, and the viscosity was found to be 170cps.

EXAMPLE 10

This experiment was conducted in the same manner as in Example 7, exceptthat a catalyst comprising 0.05 wt % of palladium and 0.3 wt % of silvercarried on an alumina carrier was used in place of the catalystcomprising 0.5 wt % of palladium carried on an alumina carrier, and thereaction time was changed to 1 hour. The reaction solution had anN-1,3-butadienylacetamide content of 1 ppm or less and contained 0.4 wt% of N-ethylacetamide. The polymerizability of the resultingN-vinylacetamide was evaluated in the same manner as in Example 1, andthe viscosity was found to be 170 cps.

EXAMPLE 11

The dimethylacetal containing 7 wt % of methanol obtained in the acetalrecovery step in Example 2 was returned to the acetal separation stepand methanol was separated from acetal. The resulting acetal contained250 ppm of 1,1,3-trimethoxybutane. This acetal was distilled using apacked column having a theoretical plate number of 20 at a ref lux ratioof 5 to obtain acetal containing 12 ppm of 1,1,3-trimethoxybutane. Theresulting acetal was subjected to the processes subsequent to thesynthesis step of 1-methoxyethylacetamide as described in Example 3.However, in this example, simple distillation was conducted in place ofrectification at the N-vinylacetalamide purification step. The resultingN-vinylacetamide contained 10 ppm of N-1,3-butadienylacetamide. Thepolymerizability of the resulting product was evaluated in the samemanner as in Example 1, and the viscosity was found to be 70 cps.

COMPARATIVE EXAMPLE 2

N-vinylacetamide was produced in the same manner as in Example 1 exceptfor omitting the rectification of acetal. The resulting N-vinylacetamidecontained 230 ppm of N-1,3-butadienylacetamide. The polymerizability wasevaluated in the same manner as in Example 1, and the viscosity wasfound to be 10 cps or less.

EXAMPLE 12

The residue on evaporation substantially comprisingN-(1-methoxyethyl)acetamide obtained in the acetal recovery step inExample 2 was distilled using a packed column having a theoretical-platenumber of 20 at a reflux ratio of 6 to obtainN-(1-methoxyethyl)acetamide containing 11 ppm ofN-(1,3-dimethoxybutyl)acetamide. The resultingN-(1-methoxyethyl)acetamide was subjected to the synthesis step ofN-vinylacetamide as described in Example 3, except that simpledistillation was conducted in place of rectification at theN-vinylacetamide purification step. The resulting N-vinylacetamidecontained 9 ppm of N-1,3-butadienylacetamide. The polymerizability wasevaluated in the same manner as in Example 1, and the viscosity wasfound to be 80 cps.

COMPARATIVE EXAMPLE 3

N-vinylacetamide was produced in the same manner as in Example 9, exceptfor omitting rectification of N-(1-methylethyl)acetamide. The resultingN-vinylacetamide contained 230 ppm of N-1,3-butadienylacetamide. Thepolymerizability was evaluated in the same manner as in Example 1, andthe viscosity was found to be 10 cps or less.

EXAMPLE 13

To a glass-made reaction vessel, 745 g of water, 250 g ofN-vinylacetamide obtained in Example 2 and 0.409 g ofN,N'-(diacetyl)-N,N'-(divinyl)-1,4-bis(aminomethyl)cyclohexane as acrosslinking agent were added and dissolved. After removing thedissolved oxygen by a nitrogen gas, 0.075 g of 2,2'-azobis2-(2-imidazolin-2-yl)propane dihydrochloride dissolved in 5 ml ofdeaerated water was added, and the mixture was insulated from heat andallowed to stand. After 7 hours, the inner temperature of the reactionvessel reached 71° C. due to polymerization heat and thereafter, theinner temperature gradually lowered due to heat loss. The time periodfrom the addition of a polymerization initiator to the time when theinner temperature of the reaction vessel reaches a maximum is called the"peak achieving time". In this example, the peak achieving time was 7hours.

COMPARATIVE EXAMPLE 4

The polymerization was conducted in the same manner as in Example 13,except that N-vinylacetamide obtained in Comparative Example 1 was usedin place of N-vinylacetamide obtained in Example 2. An increase of innertemperature accompanying the polymerization was not observed even after48 hours from the addition of the polymerization initiator.

EXAMPLE 14

To a glass-made reaction vessel, 745 g of water, 225 g ofN-vinylacetamide obtained in Example 2 and 27.6 g of sodium acrylatewere added and dissolved. After removing the dissolved oxygen by anitrogen gas, 0.075 g of 2,2'-azobis 2-(2-imidazolin-2-yl)propanedihydrochloride dissolved in 5 ml of deaerated water was added, and themixture was isolated from heat and allowed to stand. The peak achievingtime was 6 hours.

COMPARATIVE EXAMPLE 5

The polymerization was conducted in the same manner as in Example 13,except that N-vinylacetamide was used in place of N-vinylacetamideobtained in Example 2. An increase of inner temperature accompanying thepolymerization was not observed even after 48 hours from the addition ofthe polymerization initiator.

EXAMPLE 15

A solution having a pH of 6.5 (determined with a 33 wt % aqueoussolution) and containing 98 wt % of N-(1-methoxyethyl)acetamide and 2 wt% of acetamide was fed in an amount of 35 g per minute into a stainlesssteel reaction tube having an inner diameter of 21 mm and a total lengthof 6 m. The reaction tube was heated to 400° C., and the pressure wasreduced to 100 mmHg. A mixture of N-vinylacetamide and methanol producedby the thermal cracking reaction was condensed in a condenser providedat the exit of the reaction tube and recovered. The N-vinylacetamidecontained 28 ppm of N-1,3-butadienylacetamide, and the conversion ofN-(1-methoxyethyl)acetamide was 85%.

The resulting reaction solution was introduced into the tenth stage fromthe top of a glass-made oldershaw-type rectification column having 10stages, in an amount of 200 g per hour. The column was heated so thatthe temperature of the column top was maintained at 40° C. at a reducedpressure of 200 mH and a reflux ratio of 2. A 500 ml-volume flask wasprovided at the lower portion of the rectification column and heated bydipping in an oil bath of 80° C. to extract the content of the flask inan amount of 155 g per hours. The solution extracted from the flask wasa crude N-vinylacetamide solution containing 94 wt % ofN-vinylacetamide. From the top of column, methanol was extracted in anamount of 45 g per hour.

The resulting crude N-vinylacetamide solution was introduced into thefifth stage from the top of a glass-made Oldershaw-type rectificationcolumn having 10 stages and subjected to rectification in a reducedpressure of 0.15 mmHg and at a reflux ratio of 3. As a result,N-vinylacetamide in a purity of 98% and having anN-1,3-butadienylacetamide content of 0.9 ppm was obtained. Thepolymerizability of the resulting N-vinylacetamide was evaluated in thesame manner as in Example 1, and the viscosity was found to be 100 cps.

REFERENCE EXAMPLE 1

From the methanol solution of N-vinylacetamide containing 28 ppm ofN-1,3-butadienylacetamide obtained in Example 15, the methanol wasremoved by distillation. After concentrating the N-vinylacetamide, thetemperature was adjusted to 50° C. and the mother solution was separatedin a high-pressure crystallizer at 1,800 kg/cm² and 50° C. As a result,N-vinylacetamide in a purity of 99.9% and containing 2 ppm ofN-1,3-butadienylacetamide was obtained. The polymerizability of theresulting N-vinylacetamide was evaluated in the same manner as inExample 1, and the viscosity was found to be 80 cps.

EXAMPLES 16 TO 19 AND COMPARATIVE EXAMPLES 6 TO 9

A reaction was conducted in the same manner as in Example 15, except forusing N-(1-methoxyethyl)acetamide containing N-vinylacetamide in variousconcentrations as a raw material. The reaction results, the contents ofN-1,3-butadienylacetamide after purification and the polymerizability ofthe N-vinylacetamide are shown together in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        N-vinyl-            Conver- N-Butadienyl-                                                                          Polymeriz-                               acetamide    33%    sion    acetamide                                                                              ability                                  (%)          pH     (%)     (ppm)    (cps)                                    ______________________________________                                        Example 16                                                                            3        6      85    2        80                                     Example 17                                                                            5        7      84    6        50                                     Example 18                                                                            7        8      86    10       30                                     Example 19                                                                            1        5      86    10       35                                     Comparative                                                                           1        4      87    50       8                                      Example 6                                                                     Comparative                                                                           3        4      87    400      5                                      Example 7                                                                     Comparative                                                                           11       8      86    40       5                                      Example 8                                                                     Comparative                                                                           13       8      86    50       5                                      Example 9                                                                     ______________________________________                                    

The crude N-vinylacetamide is obtained, for example, (1) bydealcoholization of an N-(1-alkoxyethyl)carboxylic acid amide, (2) bydealcoholization of an N-(1-alkoxyethyl)carboxylic acid amide obtainedas an intermediate from carboxylic acid amide, acetaldehyde and alcoholor from carboxylic acid amide and acetaldehyde dialkylacetal, or (3) bycracking ethylidene biscarboxylic acid amide or by cracking anethylidene biscarboxylic acid amide obtained as an intermediate fromacetaldehyde and carboxylic acid amide. The crude N-vinylacetamideobtained by these known production processes does not have goodpolymerizability. However, when the N-1,3-butadienylcarboxylic acidamide content in the crude N-vinylcarboxylic acid amide is reduced to 30ppm or less, preferably 10 ppm or less, more preferably 1 ppm or less,and then the crude vinylcarboxylic acid amide is subjected to apurification process, a highly polymerizable N-vinylcarboxylic acidamide having improved polymerizability is obtained.

Furthermore, the N-1,3-butadienylcarboxylic acid amide can be reduced tothe above-described content range by subjecting a crudeN-vinylcarboxylic acid amide or solution thereof to a purificationprocess such as a rectification method, a recrystallization method, apressure crystallization method, a physical adsorption method using anactivated carbon adsorbent, a Diels-Alder reaction method or a selectivehydrogenation reaction method of a 1,3-butadienyl group.

Furthermore, according to the present invention, in producingN-vinylcarboxylic acid amide by thermal cracking or catalytic crackingof N-(1-alkoxyethyl)carboxylic acid amide or ethylidenebiscarboxylicacid amide, a highly polymerizable N-vinylcarboxylic acid amide can beobtained. Furthermore, a polymer of a high molecular weightN-vinylcarboxylic acid amide can be produced using the highlypolymerizable monomer.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A homopolymer of N-vinylcarboxylic acid amide ora copolymer thereof with another copolymerizable monomer having a weightaverage molecular weight of 500,000 or more, prepared by polymerizing ahighly polymerizable N-vinylcarboxylic acid amide having anN-1,3-butadienylcarboxylic acid amide content of 30 ppm or less.
 2. Theproduct of claim 1, having a weight average molecular weight of1,000,000 or more.